Icemaker control system

ABSTRACT

A control system for an icemaker utilizes a control scheme in which various operating conditions of the icemaker are monitored sand the icemaker is shut down if a fault condition is sensed. In response to detection of the fault condition, steps are taken to actively remove the fault. Restarting of the icemaker is then attempted if sensors indicate that normal continued operation should be possible. The operating conditions sensed include the temperature of refrigerant at an outlet from a condenser, the rate at which a water pan fills with water while water is delivered to it for subsequent delivery to and over an evaporator to freeze the water into ice on the evaporator. and the time required to harvest ice from the evaporator.

This application claims benefit of provisional application Ser. No.60/455,103, filed Mar. 13, 2003.

FIELD OF THE INVENTION

The present invention relates to commercial icemakers, and in particularto control systems therefore.

BACKGROUND OF THE INVENTION

Commercial ice making machines are well known in the art and provide forthe manufacture of ice in various forms, such as cubed and flaked. Cubetype icemakers typically make ice by running a flow of water over avertically oriented evaporator until ice of a sufficient thickness hasformed thereon. When the ice is of harvest size, a hot gas defrostingprocedure is typically used to remove the ice from the evaporator. Ithas long been recognized that icemakers are prone to a variety ofmalfunction events. In response thereto icemakers were first designed toinclude different control systems that shut down the icemaker inresponse to a sensor indicating that a problem exists. Examples of suchmalfunctions include the condenser being too cold or too hot, ice notbeing successfully harvested from the evaporator, or insufficient waterin the water pan. It is also well understood that certain of themalfunctions can be due to causes that are transient in nature. Thus,control strategies have been proposed that allow the ice machine to shutdown if a problem is sensed and then to restart and attempt to againmake ice. In case the malfunction is not due to a transient problem,these restarts are usually limited to some predetermined number so thatthe icemaker does not vainly attempt an unlimited number of restarts. Itis also well known to add a time delay between each restart in order toincrease the total time period over which the limited number of restartsis attempted. This approach can provide more time for the transientproblem to go away, while not increasing the number of restarts. At theend of the number of predetermined restart attempts after which a normalcycle of functioning is not restored, it is known to put the machineinto a permanent shut-down and activate an indicator light to summon aservice technician. Likewise, it is known to reset the counting ofrestarts to zero if a full ice making cycle results and is followed by asuccessful harvest.

A problem with the foregoing control approaches is that the restartssimply occur right after the error is sensed or after the predeterminedtime delays. In either case, the restart is essentially “mechanical”,that is, without any regard to the actual conditions of the machine.Thus, as long as the particular problem that initiated the shut downcontinues to exist, each restart attempt during that time is futile andcan result in a needless waste of water and/or energy. Efficiency ofenergy and water use is of critical concern to owners and operators ofice making machines. Accordingly, it would be very desirable to have acontrol system that is better responsive to the actual operatingcondition of the ice maker so that restart attempts are minimized andare only initiated when there is a greater chance of a successful icemaking cycle occurring. A further problem with the prior art controlsconcerns the fact that nothing is done in an attempt to actively removeor clear the problem causing the fault condition. Restart attempts aresimply repeated in hopes that the error condition goes away or issomehow eliminated by the restart process itself Thus, it would also bedesirable to have a more active control strategy that can take specificand more positive steps to eliminate an error condition.

SUMMARY OF THE INVENTION

The present invention concerns a control system for an ice maker whereinvarious operating condition thereof are continually monitored and wherethe ice maker is shut-down if a fault condition is sensed. A restart isattempted if sensors indicate that normal continued operation should bepossible. Also, certain control steps are taken to actively remove theerror condition.

A condenser routine is shown wherein operation of the ice maker isdiscontinued if a predetermined high temperature thereof is sensed. Theice maker is only restarted when a suitably low condenser temperature issensed indicating that a subsequent full cycle ice making operation isattainable. If the predetermined high temperature is nevertheless againencountered, the control will again shut-down the ice maker and waitagain for the desired low temperature to be sensed. A predeterminednumber of theses restarts will result in a permanent shut down conditionbeing instructed. Thus, the control of the present invention does notattempt a restart unless and until the condenser temperature has comedown to a predetermined low temperature. Thus, the restart has a muchgreater likelihood of leading to a successful completion of an icemaking cycle.

A water fill rate routine is shown wherein a sensor monitors the rate offilling of a water pan below the evaporator. If the fill rate fallsbelow a predetermined rate, the ice maker shuts off the compressor andthe fill valve remains on. Once the rate increases above thepredetermined rate or the high level is obtained, the compressor turnson, and the ice maker resumes a normal ice making cycle. If the waterfill rate goes below a predetermined low fill rate the ice maker is shutoff and water filling is discontinued. In this manner the control of thepresent invention conserves energy by turning off the compressor if thewater fill rate is low but otherwise acceptable. The compressor is thenrestarted when the water does eventually reach the desired full level.

A failed harvest routine is shown and requires the monitoring of one ormore proximity switches associated with a curtain that is pivotallypositioned adjacent the evaporator. If ice is successfully harvestedfrom the evaporator, it will fall there from into an ice bin therebelow, and in doing so, will contact and move the curtain to an openposition. If the one or more curtain proximity switches do not all openin 4 minutes, thereby indicating a failed harvest, the compressor andhot gas valve shut off. The fill valve opens, allowing new warm water toenter the system and the circulating pump then runs for 10 minutescirculating that water over the evaporator. The control then causes theice maker to enter into a hot gas cycle wherein hot gas from thecompressor is sent through the evaporator. The control keeps track ofthe repeated failed harvests until a predetermined maximum value isreached and then stops any further restart attempts. Therefore, thecontrol of the present invention includes the further and moreaggressive steps of circulating warm water over the evaporator in orderto more effectively dislodge ice that is resistant to being successfullyharvested from the evaporator.

DESCRIPTION OF THE DRAWINGS

A better understanding of the construction and operation of the presentinvention as well as the objects and advantages thereof can be had byreference to the following detailed description which refers to thefollowing figures, wherein:

FIG. 1 shows a perspective view of an ice maker mounted atop an icestorage bin.

FIG. 2 shows a partial cross-sectional view of the interior of the icemaker.

FIG. 3 shows a schematic representation of the ice maker.

FIG. 4 shows an enlarged view of the ice maker control board.

FIG. 5 shows an enlarged partial cross-sectional view of the water panand pressure fitting.

FIGS. 6A and 6B show a flow diagram of the general control strategy ofthe present invention.

FIG. 7 shows a flow diagram of the condenser control routine of thepresent invention.

FIG. 8 shows a flow diagram of the water fill control routine of thepresent invention.

FIG. 9 shows a flow diagram of the failed harvest control routine of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The ice maker of the present invention is seen in FIG. 1, and referredto generally by the numeral 10. Ice maker 10 includes an exteriorhousing 12 and is positioned atop an insulated ice retaining bin 14. Asis further understood by referring to FIGS. 2 and 3, and as isconventional in the art, ice maker 10 includes a vertical ice formingevaporator plate 16, a condenser and fan 18 and a compressor 20connected by high pressure refrigerant lines 21 a and low pressure line21 b. As is also well understood, the refrigeration system hereinincludes an expansion valve 22 and a hot gas valve 24. A water catchingpan 26 is positioned below evaporator 16 and includes a partial cover27. A water distribution tube 28 having a water inlet 29 extends alongand above evaporator 16. A water supply solenoid valve 30 has an inletconnected to a source of potable water, not shown, and an outlet line 31supplying water to pan 26. A water pump 32 provides for circulatingwater from outlet 32 b thereof to inlet 29 of distribution tube 28 alonga water line 34.

A solenoid operated dump valve 36 is fluidly connected to line 34 andserves, when open, to direct water pumped thereto to a drain, not shown.An evaporator curtain 37 is pivotally positioned closely adjacentevaporator 16 and includes a magnetic switch 38 for indication when ithas moved away from evaporator 16 to an open position indicated by thedashed line representation thereof. For purposes of clarity of the viewof FIG. 2, the various fluid connections of pump 32, dump valve 36 andwater supply valve 30 are not shown, such being represented in schematicform in FIG. 3.

As particularly seen in FIG. 4, and also by referring to FIG. 2, anelectronic control board 40 is located within a separate housing 41 at aposition remote and physically isolated from pan 26 and evaporator 16.Control board 40 includes a microprocessor 42 for controlling theoperation of ice maker 10. Board 40 includes a pressure sensor 44, suchas manufactured and sold by Motorola, Inc. of Phoenix, Ariz., andidentified as model MPXV5004G. As understood by also viewing FIG. 5, aplastic pneumatic tube 46, shown in dashed outline, is connected tosensor 44 and on its opposite end to a cylindrical air cup or fitting48. Those of skill will understand that housing 41 includes a cover, notshown, that provides for the enclosing and protection of control 40 andsensor 44 therein and through which tube 46 passes prior to connectingto sensor 44. A temperature sensor 47 is positioned on the outletrefrigerant line of condenser 18 and is connected to control 40.

Fitting 48 resides in pan 26 at the bottom thereof and is press fitwithin a circular ridge 49 that is formed as an integral molded portionof the bottom surface of pan 26. Fitting 48 includes an outer housing 48a defining an inner air trapping area 48 b and a tube connecting portion48 c. Four water flow openings 50 exist around a bottom perimeter ofhousing 48 a.

The operation of the present invention can be better understood byreferring to the flow diagram of FIGS. 6A and 6B wherein the basicoperation of the present invention is shown. At start block 51 power isprovided to control 40. At block 52 compressor 20 is turned on andsubstantially simultaneously at block 54 fill valve 30 and dump valve 36are opened. Thus, cooling of evaporator 18 begins and water flows intopan 26. At decision block 56, once a predetermined pump-on water levelis reached in pan 26, as indicated by the level line represented by theletter P in FIG. 5, circulatory water pump 32 is turned on at block 58.The pump-on point is sensed by sensor 44. In particular, as water fillspan 26, water flows through holes 50 of fitting 48. As that occurs, airtrapped in area 48 b is slightly compressed and forced into tube 46which communicates such pressure increase to sensor 44. That pressure isthen input as a voltage to microprocessor 42 which assigns a numericalvalue thereto corresponding to a pressure scale. Therefore, when thepredetermined pressure value is sensed that corresponds to the pressureat level P, pump 32 is turned on. Because of the fluid connections ofpump 32 and dump valve 36, the action of pump 32 serves to move anywater in pan 26 to valve 36 causing the draining away thereof. Thus, aminimum water level, indicated by the level line represented by theletter M in FIG. 5, is sensed in the same manner as described above forlevel P. When that predetermined volume of the water has been removedfrom pan 26, pump 32 is stopped at block 62. As the water supply valveremains on, the level in pan 26 begins to rise and when the P level isagain sensed at block 64, then at block 66, pump 32 is re-started andfill valve 30 closed. As dump valve 34 remains open, water will again bepumped from pan 26. At block 68 control 40 again senses for theattainment of the M level. When that occurs, then, at block 70, waterpump 32 is stopped, dump valve 34 is closed and fill valve 30 is opened.It can be appreciated that blocks 52-68 serve as a dump cycle wherebyany contaminants that have accumulated in pan 26 are agitated by theaction of pump 32 and the inflow of water and are twice flushed in thismanner and removed from the system.

At block 72 control 40 monitors for the attainment of a maximum filllevel for pan 26 indicated by the level line denoted by letters MX. Whenthis highest pressure level is sensed, then at block 74 fill valve 30 isclosed. At block 76, a 45 second clock is initiated to provide for somepre-cooling of the water delivered to pan 26 through flow overevaporator 16. At block 78 pump 32 is again turned on. A further 45second clock is set at block 80, and when that has timed out, fill valve30 is opened. It will be understood by those of skill that action ofpump 32 will serve to fill fluid line 34 and distribution tube 28 whichwill slightly lower the level of water in pan 26 below that of thedesired maximum water volume indicated by level MX. Thus, fill valve 30is opened at block 82, to replenish that volume as is determined atblock 84. At block 86, fill valve 30 is closed when the desired startingmaximum level MX is again attained.

At this point pump 32 is operating to flow water over evaporator 16 assuch is being cooled by the action of compressor 20, condenser and fan18 and expansion valve 22, all as operated by control 40. As ice formson evaporator 16, the water level in pan 26 goes down as does thepressure sensed by sensor 44. When a predetermined harvest water levelis reached, as indicated by the level line denoted H, a correspondingpredetermined pressure value is sensed by control 40 at block 88. Whenthe harvest point is indicated, pump 32 is stopped and hot gas valve 24is opened at block 90, causing evaporator 16 to warm resulting in therelease of the ice slab formed thereon. Of course, those of skill willunderstand that other heating means known in the art could be employed,such as, an electrical heater integral with the ice forming evaporator.As is well understood, when the slab of ice falls from evaporator 16,curtain 37 is opened and switch 38 is closed, signaling to the control40 the release of the ice slab from evaporator 16. As is also known, toinsure that the slab of ice has fallen into bin 12 and is no longer inthe vicinity of evaporator 16, at block 96, the control herein awaitsthe remaking of switch 38 which occurs when curtain 36 is free to swingback to its normal closed position unobstructed by any ice. At block 98the control returns to start and initiates a further ice making cycle.

It was found that the pressure-based water level sensing as describedherein provides for very accurate and repeatable determination andcontrol thereof, and hence, for very reliable control of the harvestcycle of an ice maker. In particular, the physical isolation of thepressure sensor 44 from pan 26 contributes to this improved performanceby serving to prevent any degradation of the sensor due to the presenceof water and/or the corrosive impact thereof.

The operation of the high condenser temperature error control can bestbe understood by reference to FIG. 7. As seen therein at block 100, icemaker 10 is in an ice making cycle where upon at block 102 thetemperature of condenser 18 is sensed by temperature sensor 47. If atblock 104 the temperature is determined to be greater than 160 degreesFahrenheit (F.) at block 106 a time period “C” is started. At block 108the condenser temperature is read again, and if at block 110 thetemperature of the condenser has gone below 160 Degrees F. normal icemaking is continued after stopping the timing of period C at block 112and resetting the time C timer at block 114. If however, at block 116time C has timed out, in the present case at 2 seconds, a counter isincremented once at block 118. At block 120 it is determined if thecounter equals three, i.e. that three successive time periods C havetimed out without a successful return to an ice making cycle and thefull completion thereof through harvest. If the C count is equal to 3,then at block 122 a high temp shut down code is flashed. All outputs arethen turned off at block 124 which then requires that ice maker 10 berestarted by a manual restart at block 126 in order to re-enter the icemaker start-up or ice making routine at block 128. If at block 120 thecount is less than three, then at block 130 a high temperature waningcode is flashed and all outputs are turned off at block 132. Thetemperature of the condenser is monitored at block 134 and if at block136 the temperature of the condenser goes to a predetermined lowtemperature, e.g. 100 degrees F., the ice malting start-up sequence isreinitiated at block 138. It can be understood that the condensertemperature error control of the present invention only reinitiates ifthe condenser temperature is deemed to have gone to a suitably lowtemperature that restart makes sense, i.e. there is a greater likelihoodthat a successful ice making cycle will ensue.

The water fill cycle control of the present invention is best understoodby referring to the flow diagram of FIG. 8. At block 200 an ice makingcycle is initiated and the control first determines at block 202 ifwater is at the maximum MX level. If it is, then at block 204 it isfirst determined that the hot gas valve 24 is closed and then at block206 the ice making cycle is entered. If at block 202 the water level isnot at the maximum, then a water fill timer is started at block 208after which valve 30 is opened at block 210. At block 212 the rate offlow in terms of inches of water depth increase in water pan 26 isdetermined by processor 42 as a function of the input of pressurecommunicated to sensor 44. If, at block 212 it is determined that thewater flow rate is increasing at a rate equal to or greater than 0.1inch per 10 seconds it is then determined at block 214 if the MX waterlevel has been reached. If that MX level has been achieved at block 214then valve 30 is closed at block 216 and the hot gas valve 24 is checkedat block 218. If valve 24 is off, then an ice making cycle is entered atblock 220. Thus, as long as the flow rate of the water entering pan 26correlates to a rate of fill of greater than or equal to 0.1 inch per 10seconds of water level increase in pan 26, ice maling proceeds once theMX level is reached. However, if at block 222 it is determined that thewater level in pan 26 is less than one quarter of an inch, then at block224 a failed water system shut down code is flashed and all outputs areturned off at block 226. A manual restart at block 228 is then requiredto re-enter the ice making routine start-up at block 230. If at block212 it is determined that the pressure increase corresponds to a fillrate of pan 26 per 10 seconds as being less that 0.1 inch at block 232the compressor is turned off and at block 234 an inlet water warning isflashed.

It can now be understood that the water safety control of the presentinvention actively looks at the fill rate of pan 26 and has a built intolerance for that fill rate. If the fill rate is above a certainpredetermined rate, the compressor is left on. If the fill rate is lowbut otherwise acceptable, i.e. the filling of the pan will occur in aslower but nevertheless reasonable period of time, then that filling isallowed to continue. However, the compressor is turned off so as not towaste energy during the longer fill cycle. The water fill routine of thepresent invention is also an improvement over the prior art wherein asimple timer is used without regard to the actual fill rate. Thus, thewater fill routine herein will not recognize as a “fault” what othersystems may otherwise determine as such based upon the simple timing outof a timer. A threshold low or no fill rate is also determined belowwhich the filling of pan 26 is exceedingly slow or not occurring at all,whereupon a manual restart should be required. If less than one quarterof an inch of water is seen in pan 26, that would indicate that no wateris flowing or that, for example, pan 28 is leaking water and notfilling.

The improved harvest cycle control of the present invention can best beunderstood in view of FIG. 9. At block 300, a harvest cycle is signaledto begin and at block 302 hot gas valve 24 is opened. A harvest timer isthen started at block 304. If, at block 306 the harvest time is lessthan four minutes and at block 308 all the proximity switches 38 areopen, indicating a successful harvest, then at block 310 a subsequentice maling cycle is entered. If at block 306 the harvest time exceeds 4minutes, then a harvest timer counter is reviewed at block 312 and ifthe count thereof equals 5, then a harvest time out shut down code isflashed at block 314. At block 316 all outputs are turned off such thata manual restart is required at block 318 in order to re-enter an icemaking cycle at block 320. If at block 312 the count is less than 5, thecounter is incremented at block 322 the compressor is turned off atblock 324, and a harvest time out warning code is flashed at block 326.At block 328 a water fill timer is started and valve 30 is opened atblock 330 letting warm water fill pan 26. If at blocks 332 and 334either the water fill timer equals 4 minutes or the water MX level isreached, then a water pump timer is started at block 336. Water pump 32is then started at block 338 and circulates the warm replacement waterover the evaporator 16. When the water pump timer reaches 10 minutes atblock 340, then the ice making restart cycle is entered at block 342.

It can be appreciated that the harvest control of the present inventionuses a novel approach to circulate warm water over the evaporator for apredetermined period of time in order to melt and remove anyrecalcitrant ice from the evaporator. Thus, the control herein takesactive measures to eliminate a fault resulting from a failed harvest,wherein ice is not seen to have fallen from the evaporator.

While embodiments of the invention have been described in detail, oneskilled in the art can devise various modifications and otherembodiments without departing from the spirit and scope of theinvention, as defined in the accompanying claims.

1. A control system for an icemaker of a type having a compressor fordelivering refrigerant to and though a condenser to an evaporator, awater pan, means for delivering water to said water pan and a pump fordelivering water from said water pan to and across said evaporator tofreeze the water into ice on said evaporator for subsequent harvestingof the ice, said control system comprising: means responsive to thetemperature of refrigerant at an outlet from said condenser beinggreater than a predetermined high temperature to interrupt operation ofsaid icemaker; means responsive to a level of water in said water panthat is less than a selected high level and to delivery of water to saidwater pan at a rate less than a predetermined rate to inhibit operationof said compressor; and means responsive during an ice harvesting cycleof said icemaker to a failure to complete harvesting of ice from saidevaporator within a selected period of time to interrupt operation ofsaid icemaker.
 2. A control system as in claim 1, wherein said meansresponsive to the temperature of refrigerant at said condenser outlet isresponsive to the temperature being greater than said predetermined hightemperature for a selected time to interrupt operation of said icemaker.3. A control system as in claim 1, wherein said means responsive to thetemperature of refrigerant at said condenser outlet includes timer meansresponsive to the temperature being greater than said predetermined hightemperature to begin timing a selected period of time, means forresetting said timer means upon occurrence of a the temperature being nogreater than said predetermined high temperature, and means responsiveto timing out of said timer means at the end said selected time periodto interrupt operation of said icemaker.
 4. A control system as in claim3, wherein said means responsive to the temperature of refrigerant atsaid condenser outlet further includes means, operative followinginterruption of operation of said icemaker upon timing out of said timermeans at the end of said selected time period, for enabling continuedoperation of said icemaker upon the temperature of refrigerant at saidcondenser outlet decreasing to a predetermined low temperature.
 5. Acontrol system as in claim 4, wherein said means responsive to thetemperature of refrigerant at said condenser outlet further includescounter means for storing a count of the number of times said timermeans times out by reaches the end of said selected time period, meansresponsive to said stored count being less than a selected number forenabling operation of said icemaker upon the temperature of refrigerantat said condenser outlet decreasing to said predetermined lowtemperature, and means responsive to said stored count reaching saidselected number for interrupting operation of said icemaker andgenerating a signal that manual intervention is required to enablecontinued operation of said icemaker.
 6. A control system as in claim 1,including means for sensing the level of water in said water pan, andmeans responsive to the sensed level of water being at said selectedhigh level to prevent delivery of water to said water pan and to enableoperation of said icemaker, and responsive to the sensed level of waterbeing less than a selected low level for inhibiting operation of saidicemaker and for generating an indication that manual intervention isrequired to enable continued operation of said icemaker.
 7. A controlsystem as in claim 6, including means for sensing, upon delivery ofwater to said water pan, the rate of filling of said water pan withwater, and means responsive to the sensed water fill rate being at leastequal to a selected rate and to the sensed water level beingintermediate said selected low and high levels for enabling operation ofsaid compressor while the sensed water level is less than said selectedhigh level, and for interrupting delivery of water to said water pan andenabling operation of said icemaker when the sensed water level reachessaid selected high level.
 8. A control system as in claim 7, whereinsaid means for sensing the rate of filling of said water pan waterincludes means responsive to changes in the sensed level of water in thewater pan with respect to time to determine the rate of filling.
 9. Acontrol system as in claim 1, including means for delivering hotrefrigerant from said condenser to said evaporator to heat saidevaporator to cause release of ice formed on said evaporator in order toharvest the ice, and wherein said means responsive to a failure tocomplete harvesting of ice from said evaporator within said selectedperiod of time includes timer means responsive to delivery of hotrefrigerant to said evaporator to beg timing said selected time period,means for sensing release of ice from said evaporator, and meansresponsive to said sensing means sensing release of ice from saidevaporator before said timer means reaches the end of said selected timeperiod to enable continued operation of said icemaker.
 10. A controlsystem as in claim 9, wherein said means responsive to a failure tocomplete harvesting of ice from said evaporator within said selectedtime period includes means responsive to failure of said sensing meansto sense release of ice from said evaporator before said timer meanstimes out at the end of said selected time period to disable operationof said compressor.
 11. A control system as in claim 10, wherein saidmeans responsive to failure to complete harvesting of ice from saidevaporator within said selected time period includes means fordelivering water to said water pan and for operating said pump to flowthe water from the water pan over said evaporator to warm and releaseice remaining on said evaporator, and for then enabling operation ofsaid icemaker.
 12. A control system as in claim 9, including countermeans for storing a count of the number of failures of said sensingmeans to sense release of ice from said evaporator before said tiermeans times out at the end of said selected time period, and meansresponsive to said counter means stored count being equal to a selectedcount to interrupt operation of said icemaker and to generate a signalindicating that manual intervention is required to enable continuedoperation of said icemaker.
 13. A control system for an icemaker of atype having a compressor for delivering refrigerant to and though acondenser to an evaporator, a water pan, means for delivering water tosaid water pan and a pump for delivering water from said water pan toand across said evaporator to freeze the water into ice on saidevaporator for subsequent harvesting, said control system comprising:means for sensing the temperature of refrigerant at an outlet from saidcondenser; and means responsive to said sensed refrigerant temperaturebeing no greater than a predetermined high temperature or greater thansaid predetermined high temperature for less than a selected period oftime for enabling continued operation of said icemaker.
 14. A controlsystem as in claim 13, including timer means responsive to said sensedrefrigerant temperature being greater than said predetermined hightemperature to begin timing said selected time period; means forresetting said timer means in response to sensing a refrigeranttemperature no greater than said predetermined high temperature beforesaid timer means times out at the end of said selected time period;means responsive to said timer means timing out at the end of saidselected time period to interrupt operation of said icemaker; and meansresponsive to said sensing means sensing a subsequent decrease inrefrigerant temperature to a predetermined low temperature to enablecontinued operation of said icemaker.
 15. A control system as in claim13, including counter means responsive to each occurrence of said timermeans timing out at the end of said selected time period to advance byone a count stored therein; and means responsive to said counter meansreaching a selected stored count to inhibit operation of said icemakerand to generate a signal indicating that manual intervention is requiredto enable continued operation of said icemaker.
 16. A control system foran icemaker of a type having a compressor for delivering refrigerant toand though a condenser to an evaporator, a water pan for being filledwith water, means for delivering water to said water pan, and a pump fordelivering water from said water pan to and across said evaporator tofreeze the water into ice on said evaporator for subsequent harvestingof the ice, said control system comprising: means for operating saidcompressor to deliver cold refrigerant to said evaporator; means forsensing the level of water in said water pan; means responsive to aselected maximum level of water in said water pan to enable operation ofsaid icemaker; means responsive to less than said selected maximum levelof water in said water pan to initiate delivery of water to said waterpan; means for sensing the rate of filling of said water pan with waterduring delivery of water; means responsive to said sensed water fillrate being at least equal to a selected rate to continue operation ofsaid compressor; and means responsive to said water level sensing meanssensing said selected maximum level of water in said water pan tointerrupt delivery of water and enable operation of said icemaker.
 17. Acontrol system as in claim 16, including means responsive to said sensedwater fill rate being less than said selected rate to interruptoperation of said compressor until said water level sensing means sensessaid selected maximum level of water in said water pan, and for thenenabling operation of said compressor and said icemaker.
 18. A controlsystem as in claim 16, including means responsive to said water levelsensing means sensing a selected minimum level of water in said waterpan to inhibit operation of said compressor and icemaker and to generatea signal indicating that manual intervention is required to enablecontinued operation of said icemaker.
 19. A control system for anicemaker of a type having a compressor for delivering refrigerant to andthough a condenser to an evaporator, a water pan for being filled withwater, means for delivering water to said water pan, and a pump fordelivering water from said water pan to and across said evaporator tofreeze the water into ice on said evaporator for subsequent harvestingof the ice, said control system comprising: means for delivering hotrefrigerant from said condenser to said evaporator to heat saidevaporator to release ice formed on said evaporator in order to harvestthe ice; timer means responsive to delivery of hot refrigerant to saidevaporator to begin timing a selected period of time; means for sensingrelease of ice from said evaporator; means responsive to sensing releaseof ice from said evaporator before said timer means times out at the endof said selected time period for enabling continued operation of saidicemaker; means responsive to a failure to sense release of ice fromsaid evaporator before said timer means times out at the end of saidselected time period for turning off said compressor, causing deliveryof water to said water pan, operating said pump to flow water acrosssaid evaporator to release ice remaining said evaporator, and thenenabling continued operation of said icemaker.
 20. A control system asin claim 19, said control system including a water pump timer forcontrolling the time for which said pump is operated to flow water fromsaid water pan over said evaporator to warm and release ice from saidevaporator before continued operation of said icemaker is enabled.
 21. Acontrol system as in claim 19, including counter means for storing acount of the number of failures to sense release of ice from saidevaporator before said timer means times out at the end of said selectedtime period, and means responsive to said counter means stored countequaling a selected count to inhibit further operation of said icemakerand to generate a signal indicating that manual intervention is requiredto enable continued operation of said icemaker.
 22. A method ofcontrolling an icemaker of a type having a compressor for deliveringrefrigerant to and though a condenser to an evaporator, a water pan, asupply line for delivering water to the water pan and a pump fordelivering water from the water pan to and across the evaporator tofreeze the water into ice on the evaporator for subsequent harvesting ofthe ice, said method comprising the steps of: controlling thetemperature of refrigerant at an outlet from the condenser to be nogreater than a predetermined high temperature by sensing the temperatureof refrigerant at the condenser outlet and, in response to the sensedtemperature being greater than a predetermined high temperature,interrupting operation of the icemaker; ensuring the availability ofsufficient water in the water pan for delivery to the evaporator duringan ice freezing cycle by delivering water to the water pan while sensingboth the level of water in the water pan and the rate at which the waterpan is being filled with water and, in response to a sensed level ofwater in the water pan that is less than a selected high level and to asensed water fill rate that less than a selected rate, inhibitingoperation of the compressor; and after water has been frozen into ice onthe evaporator, monitoring completion of a cycle of harvesting ice fromthe evaporator upon delivery of hot refrigerant from the condenser tothe evaporator to warm the evaporator to release the ice from its bondto the evaporator, by sensing release of the ice from the evaporatorand, if release of the ice from the evaporator is not sensed within aselected period of time, interrupting operation of the icemaker.
 23. Amethod as in claim 22, wherein controlling the temperature ofrefrigerant at the condenser outlet includes the step of measuring thetime for which the sensed refrigerant temperature is greater than thepredetermined high temperature, said interrupting step being responsiveto the sensed temperature being continuously greater than thepredetermined high temperature for a selected time to interruptoperation of the icemaker.
 24. A method as in claim 23, whereincontrolling the temperature of refrigerant at the condenser outletincludes the further steps, following performance of said interruptingstep, of sensing a decrease in the temperature of refrigerant at thecondenser outlet to a predetermined low temperature and, in responsethereto, enabling continued operation of the icemaker.
 25. A method asin claim 24, wherein controlling the temperature of refrigerant at thecondenser outlet includes the further steps of storing a count of thenumber of times said icemaker operation interrupting step is performedand, upon the stored count equaling a selected number, interruptingoperation of the icemaker and generating a signal indicating that manualintervention is required to enable continued operation of the icemaker.26. A method as in claim 22, wherein ensuring the availability ofsufficient water in the water pan for delivery to the evaporator duringan ice freezing cycle includes the steps, performed in response to saidsensing step sensing that the level of water in the water pan is at aselected high level, of interrupting delivery of water to the water pan,and enabling operation of the icemaker, as well as the steps, performedin response to said sensing step sensing that the level of water in thewater pan is less than a selected low level, of inhibiting operation ofthe icemaker and generating an indication that manual intervention isrequired.
 27. A method as in claim 22, wherein ensuring the availabilityof sufficient water in the water pan for delivery to the evaporatorduring an ice freezing cycle includes the further steps, performed inresponse to said sensing step sensing that the rate at which the waterpan is being filled with water is at least the selected rate and thatthe level of water in the water pan is intermediate a selected low leveland the selected high level, of enabling operation of the compressor andcontinuing to deliver water to the water pan, and interrupting deliveryof water to the water pan and enabling operation of the icemaker whenthe sensed water level reaches the selected high level.
 28. A method asin claim 22, wherein monitoring completion of a cycle of harvesting icefrom the evaporator includes the further steps, in response to a failureto sense release of the ice from the evaporator within the selected timeperiod, of delivering water to the water pan, operating the pump to flowthe water from the water pan over the evaporator to warm and release iceremaining on the evaporator, and then enabling operation of theicemaker.
 29. A method as in claim 28, wherein monitoring completion ofa cycle of harvesting ice from the evaporator includes the further stepsof storing a count of the number of times failures to sense release ofthe ice from the evaporator within the selected time period during iceharvesting and, in response to the stored count reaching a selectedcount, interrupting operation of the icemaker and generating anindication that manual intervention is required to enable continuedoperation of the icemaker.
 29. A method of controlling an icemaker of atype having a compressor for delivering refrigerant to and though acondenser to an evaporator, a water pan, a supply line for deliveringwater to the water pan and a pump for delivering water from the waterpan to and across the evaporator to freeze the water into ice on theevaporator for subsequent harvesting, said method comprising the stepsof: sensing the temperature of refrigerant at an outlet from thecondenser; and enabling operation of the icemaker in response to asensed temperature of refrigerant that is no greater than apredetermined high temperature or that is greater than the predeterminedhigh temperature for less than a selected time.
 30. A method as in claim29, including the further steps of: interrupting operation of theicemaker in response to a sensed refrigerant temperature that is greaterthan the predetermined high temperature continuously for a selectedtime; and enabling continued operation of the icemaker, followingperformance of said interrupting step, in response to a sensed decreasein refrigerant temperature to a predetermined low temperature.
 31. Amethod as in claim 29, including the further steps of: storing a countof each occurrence of a sensed refrigerant temperature that is greaterthan the predetermined high temperature continuously for the selectedtime; and in response to the stored count reaching a selected count,inhibiting operation of the icemaker and generating an indication thatmanual intervention is required to enable continued operation of theicemaker.
 32. A method of controlling an icemaker of a type having acompressor for delivering refrigerant to and though a condenser to anevaporator, a water pan, a supply line for delivering water to the waterpan and a pump for delivering water from the water pan to and across theevaporator to freeze the water into ice on the evaporator for subsequentharvesting of the ice on the evaporator, said method comprising thesteps of: operating the compressor to deliver cold refrigerant to theevaporator; sensing the level of water in the water pan; enablingoperation of the icemaker in response to a sensed maximum level of waterin the water pan; delivering water to the water pan in response to asensing less than the maximum level of water in the water pan; sensingthe rate of filling of the water pan with water during deliver of waterto the water pan; continuing operation of the compressor in response tothe sensed water fill rate being at least equal to a selected water fillrate; and interrupting delivery of water to the water pan and enablingoperation of the icemaker in response to sensing the maximum level ofwater in the water pan.
 32. A method as in claim 32, including thefurther steps of; interrupting operation of the compressor upon thesensed water fill rate being less than the selected fill rate whilecontinuing to deliver water to the water pan; and enabling operation ofthe icemaker upon the sensed level of water in the water pan reachingthe selected maximum level.
 34. A method as in claim 32, including thesteps of inhibiting operation of the icemaker and, in response tosensing a selected minimum level of water in the ice pan, generating anindication that manual intervention is required to enable continuedoperation of the icemaker.
 35. A method of controlling an icemaker of atype having a compressor for delivering refrigerant to and though acondenser to an evaporator, a water pan, a supply line for deliveringwater to the water pan and a pump for delivering water from the waterpan to and across the evaporator to freeze the water into ice on theevaporator for subsequent harvesting of the ice on the evaporator, saidmethod comprising the steps, at the end of an icemaking cycle when waterhas been frozen into ice on the evaporator, of: delivering hotrefrigerant from the condenser to the evaporator to heat the evaporatorto release the ice from the evaporator; sensing release of the ice fromthe evaporator; enabling continued operation of the icemaker in responseto sensing release of the ice from the evaporator within less than aselected time following delivery of hot refrigerant to the evaporator;and in response to failing to sense release of the ice from theevaporator within the selected time, performing the steps of turning offthe compressor, delivering water to the water pan, operating the pump toflow water from the water pan to and across the evaporator to warm andrelease ice remaining on the evaporator, and then enabling operation ofthe icemaker.
 36. A method as in claim 35, wherein the step of flowingwater across the evaporator to release ice from the evaporator flows thewater across the evaporator for a selected time.
 37. A method as inclaim 35, including the steps of storing a count of the number offailures to sense release of the ice from the evaporator within theselected time following delivery of hot refrigerant to the evaporatorand inhibiting further operation of the icemaker and, in response thestored count reaching a selected count, generating an indication thatmanual intervention is required to enable continued operation of theicemaker.